From San Jose, catch the MEPE (Costa Rica's national bus line) bus to Puerto Viejo. There are about four buses per day, with the first leaving at 6 a.m. It's a 4-1/2 hour ride and the cost is about $8 U.S. Dollars. Try to buy your tickets a day or two ahead of time because the buses sometimes sell out.
The bus terminal for this trip is Terminal Caribe, which is about four blocks north of downtown on Calle 13. It's just northeast of the big Children's Musem in San Jose.
Make sure you buy tickets for Puerto Viejo, Talmanaca, or Puerto Viejo, Limon. There is another Puerto Viejo in Costa Rica -- a little inland town on the Sarapaqui River, and that's not where you want to go. If there's a doubt, tell them you want to go to Puerto Viejo "en la playa" (at the beach).
Mepe has good reliable service to San Jose but it is still a relatively long trip. A few things I have done to make it easier.
a) If you are planning to take a rafting trip, do it on your way out of PV. I did a rafting trip on the Pacare River. The excursion bus picks you up in PV and takes you to the river. Another bus will take you into San Jose when you are done. This breaks the long trip into two manageable parts.
b) Take an hour or two in Limon. You can take the local bus into Limon, walk around town, then get a Limon-San Jose bus. The advantage here is that the Limon bus line uses much nicer buses than Mepe and they are more frequent runs. Note however there are two bus terminals in Limon, one for the local runs down the coast, and one for SJ. They are easy walking distance but you may need to ask directions. Street signs are hard to find.
c) Take the earliest bus you can manage. Its an easier drive in the cooler hours of the morning.
d. Make sure you use the Mepe rest stop in Limon to good advantage. use the washroon, walk around and stretch your legs.
e. Take it easy the night before. There is enough shake, rattle, and roll to make a hangover a real nightmare.
There are plenty of bike rental places all aropund town. $3/day is the going rate
When renting a bicycle make sure that the tires are well inflated, chain is greased, and ask if someone will pick you up if there is a problem with the bike.
The public bus is cheap, easy, and fast
Puerto Viejo to Cahuita is about $1
Puerto Viejo to San Jose is about $8
Tickets for the bus can be purchases at the building across from the bus stop in Puerto Viejo
Rent a bike in Puerto Viejo and take day trips to Manzanillo, Punta Uva, and Cahuita. Manzanillo and Cahuita are about 16 kilometers one way, and the ride is relatively flat. It tends to get a bit hillier right before you hit Manzanillo however and your quads will start to burn. Oh yeah.
If you are especially lazy or not bike-inclined, take the bus, hitch a ride (like many do), take a taxi, or heck even just walk.
It shouldn't cost more than 5 dollars to rent a bike for the entire day in Puerto Viejo. There are rentals available all over town. Just don't rent a decrepit one like mine. It had no handlebar grips, so my palms were raw by the end of the day. And with only one speed, it was a pain to get to the top of some steep hills.
There are lots of bike rental shops around town . It´s pretty cheap to rent for a day or longer and its a good way to get around town or to the other beach areas!